12 Tips on How to Repair Spalled Concrete

Those Rebars Might Be the Reason for Concrete Spalling

Spalled concrete
Spalled concrete. Photo nakmsm Flickr

From time to time, you can receive calls from a customer asking why the concrete is flaking and how this can be solved. Spalling concrete can look like round or oval depressions along concrete surfaces or joints. This type of problem can be more frequent in colder environments when de-icing chemicals are applied or can be happening because of the freeze-thaw cycles.

Why It Happens and How to Avoid It

Spalls can appear because the rebar has been exposed and the humidity and water have started to rust the rebar or maybe because the concrete joints were improperly built.

As weather changes, the concrete will expand causing it to spall and to deteriorate even more. One key aspect that can prevent the concrete from spalling is to apply a good water sealant to the finished surface, preventing water from entering into the concrete.

Spalls can actually be avoided if the concrete is managed carefully and following appropriate techniques when it is being poured. A good way to prevent concrete from spalling is providing an adequate concrete cover to rebars and placing joints at the right locations and at the right distances. One key factor to consider also, is the concrete mix, as the water content might also trigger this condition. Pay special attention to the edges of exposed concrete and at the corners to provide an adequate concrete cover as specified by your structural engineer or the ACI. 

How to Fix Concrete Spalling

Depending on how severe the condition is, the solution might require some more or less labor intensive repairs.

These are the best ideas on how to fix spalled concrete.

  • When the concrete is damaged shallower that 1/3 of is thickness, then it shall be repaired but when it is deeper than 1/3, steel bars might be installed and a full depth restoration might be needed.
  • When the rebars are exposed and are corroded, be sure to clean them before starting the restoration process. Using a wire brush clean the steel bars thoroughly and apply a protective coating to prevent this from happening.
  • When the problem is over a driveway or horizontal surfaces such as plazas and/or sidewalks, a cementitious overlay might need to be applied. After the overlay has set completely, a waterproofing membrane should be applied to prevent the spalling from happening.
  • For an effective repair process, be sure to remove concrete to a depth of at least 1.5 inches. Clean and remove all debris before starting.
  • Patching might be done extending at least 4 inches beyond the concrete spalling area.
  • For better results, saw cut a rectangular section of concrete so the patching can be done and the concrete can be contained within the area.
  • Clean and remove all debris and fine particles from the concrete before patching. If needed clean with some water and remove the water with a sponge. Wait until the surface is dry before applying any compound or patching.
  • Ideally, the old concrete surface must be rough allowing for a better bonding surface.
  • Best patching materials are portland-cement-based or epoxy.
  • Patch materials shall be mixed taking into consideration that these compounds can dry or react fast, so just mix what you are planning to use in 15 minutes.
  • Make sure the air temperature is over 40 degrees Fahrenheit, otherwise, the patching material might not work.
  • Use only materials with an expansion coefficient similar to that of the concrete
  • If a joint needs to be repaired, it must be restored properly to allow for expansion of the concrete slab. 

Materials Used to Fix Spalled Concrete

In addition to the rust inhibitor material that should be applied over rusted steel rebars, you can get some very good product to repair spalled concrete. Some of the most recommended manufacturers are:

There are many other products and tools available to fix this problem, and always read manufacturer's recommendation before proceeding.